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Yamaha EMX312SC Mixer no low end sound

I am trying to repair a Yamaha EMX312SC Mixer which suddenly lost all bass/ low end whilst in use. It had two speakers plugged into it at the time and continued to output the mids and highs so I have assumed that it is the mixer and not the speakers at fault. So far I have dissembled the mixer following the attached service guide (though have not dissembled the power supply half of the mixer yet) and have not seen any obvious faults/ blown components etc.

Does anyone have a similar experience ? Any ideas? Also in the service guide are several circuit diagrams. If someone could identify the circuitry responsible for the low end audio that would be very kind because I have very little experience with audio circuity.

It had two speakers plugged into it at the time and continued to output the mids and highs so I have assumed that it is the mixer and not the speakers at fault.

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You have probably assumed wrongly, the most likely cause of the problem is that you've blown the bass units in the speakers - it's very unlikely to be a fault in the amplifier, which doesn't process bass and mid/high separately.

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Thanks for the reply. The amp has a built in limiter so would it not be fairly unlikely to blow both speakers at once?

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It depends on your faith in limiters!

There's very little in the amp that could cause lack of bass on both channels, while speaker failure is pretty common and would cause what you're getting. Some speakers even have internal fuses which may have blown?.

It's simple to check - either try the speakers on a different amp - a home HiFi would do. Or try different speakers on this amp - again, home HiFi speakers would 'do', BUT only at very low volume, and whilst being very careful.

Failing that, apply a 9V battery across the speaker - you should hear a fairly substantial 'THUD' and see the bass cone move a good amount. You use a 9V battery because it's what you can borrow out of an effect pedal when you're at a gig

I've been a professional service engineer for over 40 years, and with a fault like this I wouldn't even consider the amp until I'd proved the speakers were OK.

Nigel is absolutely right, it's far more likely the speakers. The only oddity is that it would be unusual to blow both speakers at exactly the same moment - although it wouldn't be that unusual to blow them both at the same gig and not notice unitll the end...
As recomended, get those speakers checked out and let us know if you've still got a problem.

Thanks to everyone who replied. Fudged some cables together in order to test the amp on another set of speakers and the amp sounded fine. Took the speakers apart and checked the resistance across the bass drivers and they have blown in both speakers! Think I'll be ordering a set of replacement drivers!